Please Suggest An Electronic Crossover

+1 to eric_squires.  Bloody hell man!, 
Unless your vintage x-covers have electrolytic caps don't f* with them! Just pass enough juice to reform those old Mylars or what have you.  Replacement of resistors if they have gone out of spec could clean thing up a bit, but an attempt to re-engineer those x-covers will likely not end well. I've owned RS-1.5 and sadly parted ways, but still have some of my best audio memories those paired with an early ps audio preamp and a highly modified dh-220  built by an EE who worked for the sound lab in Groton CT. .

What could happen ....

I have used the Parts Express DSP-408 with good results. Offers a big slice of what mini-DSP does for next to no money.  Experiment with that and see if you think you’re making progress. You’d have to break out the woofer input to direct couple it. I agree that leaving the rest of the speaker xover for now is a good phase 1 plan. I have also used HHHF as a resource and Tony is great to deal with. Have fun!

+1 jrpnde

I use a Marchand Electronic Crossover.  Amazing piece, built entirely to your spec.  Think seriously about bi-amping, purchase another amp.

But, at any rate, check out Marchand, it will give you an excellent idea of what is possible.

https://www.marchandelec.com/

Well truthfully, those old Infinity crossovers sucked due to how they were optimized.  They were optimized for frequency but not impedance I suspect in large part due to the tools available at the time.  Very demanding for amplifiers but they don't need to be.

They don't need upgraded parts.  They usually need a complete re-think. I know this is anathema, but this is a case where a good modern crossover builder with better tools can come up, and they have, with much better circuits, but to do this you need to know how to analyze a speaker.  Most arm chair speaker hobbyists don't and it's a long learning curve. 

If the problem is in the bass, my suggestion to use a hybrid set up can resolve your issues without adding too many phase/impedance/slope matching problems which all crossovers ( line level or speaker level) have. 

Maybe look online to see if you can find a person selling new crossovers with better impedance characteristics is also a good option for the Infinities.